The present invention relates to work machine power trains, and more specifically to parking lock systems for such power trains.
In the field of work machines, the power train plays an important role in propelling the work machine at appropriate speeds and providing sufficient torque for work machine movement and additional power requirements such as agricultural processing. An important feature of the work machine power train is to have a parking lock which positively locks the power train, and hence the work machine, in place. Typically, this is done by utilizing teeth on one of the power train output shafts and a parking pawl that is moveable into engagement with the teeth to positively lock the work machine in place. U.S. Pat. No. 6,250,433 discloses a positive locking parking brake where the brake/lock pin is preferably spring biased towards its extended position, with its spring acting direct on the pin.
The parking lock pawl is equipped with safety features to prevent engagement while a work machine is moving. In addition, the parking feature is operator actuated by moving an operator lever into a fixed parking lock position. With a solid link in the mechanism between the operator lever and the parking lock pawl, if the alignment of the shaft is such that the pawl engages the top of a tooth, the operator must move the work machine so that the tooth rotates out of interference with the pawl and permit engagement. This adds additional complexity to the procedure for parking the work machine, since the operator must continue to exert force on the lever engaging the parking lock mechanism.
It has been proposed to alleviate this condition by incorporating a telescoping spring loaded link within the actuation system for the parking lock. This approach, however, presents a problem when incorporated in the agricultural work machine environment with external contaminants and widely varying conditions. The clearances in a telescoping link are stringent and can be prone to sticking or other interference. In addition, the telescoping link can be misaligned when the work machine is on a hill, in which case the weight of the work machine is translated into force against the link.
What is needed in the art therefore, is a simplified and robust pre-selection mechanism for the parking lock system of a work machine power train.